尘埃遮蔽的Starburst-AGN复合星系的能谱研究
文献类型：学位论文
| 作者 | 韩云坤
|
| 学位类别 | 博士 |
| 答辩日期 | 2012-05-25 |
| 授予单位 | 中国科学院研究生院（云南天文台） |
| 授予地点 | 北京 |
| 导师 | 韩占文 |
| 关键词 | 星系：形成 星系：演化 星系：星际介质 星系：星暴 星系：活动 辐射转移 方法：数据分析 |
| 其他题名 | On the spectral energy distributions of dust-obscured Starburst-AGN composite galaxies |
| 学位专业 | 天体物理 |
| 中文摘要 | 由于激烈的恒星形成活动和超大质量黑洞的吸积活动耦合在一起同时进行，尘埃遮蔽的Starburst-AGN复合星系代表了星系的形成和演化过程中的一个重要阶段，并且是认识Starburst-AGN联系的理想实验室。 能谱分布（SEDs）蕴含了关于这类有趣的天体中恒星形成、星族和AGN活动等方面的丰富信息。 然而，通过能谱的分析来有效地提取这些物理信息在目前仍然是一个非常困难的问题。 本文首先从星系能谱分布的基本概念、多波段能谱的观测、星系能谱分布的理论模型、星系能谱分布的分析（或拟合）方法等方面对此研究领域做了系统性的介绍。 之后，本文重点介绍了我们在这个领域内所做的一些工作。 AGN的光度函数是帮助人们认识AGN活动及其演化的一个重要的可观测量。 在实践中，AGN光度函数的测量需要相互独立且各自都存在一定局限性的不同波段的观测。 为了准确地测量AGN的光度函数，我们需要结合多波段的观测以得出一个自洽的结果。 有鉴于此，基于一个改进的AGN能谱模型，我们给出了AGN的硬X-ray光度函数和IR光度函数的一个详细的比较。 我们发现，从硬X-ray光度函数出发而利用AGN能谱得出的相应IR光度函数倾向于低估高IR光度的AGN的数量。 这种低估的情况独立于AGN的硬X-ray光度函数的选择，并且对最新的硬X-ray光度函数还更加明显。 我们表明，在观测上独立获得的AGN的硬X-ray光度函数和IR光度函数之间的这种不一致可以通过在AGN的能谱模型中适当考虑进UV到X-ray的斜率$\alpha_{\mathrm{ox}}$与UV光度$L_{\rm UV}$之间的反相关而在很大程度上得到解决。 另外，我们也讨论了以上的这种不一致的其它可能解释，例如在现有的X-ray观测中遗漏的大量康普顿厚的AGN、寄主星系中恒星形成过程对mid-IR的贡献等。 与此同时，我们发现，如果假设Quasars和Seyferts这两类不同的AGN周围的遮蔽介质按不同的方式分布和演化，那么AGN的硬X-ray光度函数和IR光度函数之间将更加一致。 这个结果与人们普遍接受的认为这两类AGN的机制存在根本的不同的观点相一致。 尘埃遮蔽的Starburst-AGN复合星系比AGN更加复杂，而其多波段能谱也更加复杂、更加难以分析。 为了能更好地认识这些复杂的星系，我们组建了BayeSED\mdash一套能利用各种能谱模型或者它们的线性叠加来对星系的能谱进行详细的贝叶斯分析的程序。 其中，人工神经网络、主成分分析、和多峰嵌套采样等方法的采用使得能谱的贝叶斯分析更加高效。 作为一个示范，我们将此程序应用于对一个超高光度红外星系样本进行详细的贝叶斯能谱分析，包括贝叶斯模型比较和参数估计。 通过利用贝叶斯证据值来对纯Starburst 、纯AGN以及两者的线性叠加Starburst+AGN三种模型进行比较，我们发现，对此样本中的星系而言，Starburst+AGN模型总是具有最高的可能性。 根据计算得出的不同模型的贝叶斯证据值以及估计的Starburst成分和AGN成分的红外光度，我们发现此超高光度红外星系样本中的星系因其主导能源的不同而分为A类和B类。 另外，通过对这两类星系的其它Starburst参数和AGN参数作的一些简单的统计相关性分析， 我们发现，A类星系中AGN周围的尘埃环中尘埃含量要比相应B类中的尘埃含量更高一些，而B类星系中Starburst区的OB型星比例更高并且分布在更大的尺度上。 这些结果是与人们当前的星系通过并和而形成和演化的整体图景相一致的。 总而言之，初步的应用表明，我们的BayeSED程序给出的结果是合理的。 因此，它可以成为一个可靠而又高效的工具，能通过对能谱的详细分析来帮助人们认识像尘埃遮蔽的Starburst-AGN复合星系这样复杂的系统。 |
| 英文摘要 | Since violent formation of stars (i.e. Starburst) and growth of SMBHs (i.e. active galactic nucleus, AGN) are coupled and ongoing together, dust-obscured Starburst-AGN composite galaxies represent important phases in the formation and evolution of galaxies, and are ideal laboratories for studying starburst-AGN connections. The spectral energy distributions (SEDs) are encoded with information about star formations, stellar populations, interstellar mediums (ISM) and AGN in these interesting objects. However, it is currently still very challenging to efficiently extract the basic physical properties of these galaxies from the analysis of their SEDs. In this thesis, we firstly described the field of the analysis of SEDs (or fitting), including the basic concept of SED, the construction of observed multi-wavelength SED of galaxies, and the methods for the analysis of SEDs. Then, we present our work on this field in detail. The luminosity function (LF) of AGN is an important observable quantity for our understanding of AGN activities and their evolution. In practice, the LFs of AGN are measured independently from different wavelength bands, all of which are suffered by different limitations. To obtain an accurate determination of the LF of AGN, multi-wavelength observations need to be combined self-consistently. Given these, we present a detailed comparison between the $2-10$ keV hard X-ray and infrared (IR) LF of AGN, by employing a simple but well tested model for the SEDs of AGN. We find that the IRLFs predicted from HXLFs tend to underestimate the number of the most IR-luminous AGN. This is independent of the choices of HXLF, and even more obvious for the HXLFs recently measured. We show that the discrepancy between the independently obtained HXLFs and IRLFs of AGN can be largely resolved when the anticorrelation between the UV to X-ray slope $\alpha_{\mathrm{ox}}$ and UV luminosity $L_{\rm UV}$ is appropriately considered in the model for the SEDs of AGN. We also discuss other possible explanations for the discrepancy, such as the missing population of Compton-thick AGN and possible contribution of star-formation in the host to the mid-IR. Meanwhile, we find that the HXLFs and IRLFs of AGN can be more consistent with each other if the obscuration mechanisms of Quasars and Seyferts are assumed to be different. This is consistent with the widely accepted idea that the mechanisms of the two types of AGN are fundamentally different. The dust-obscured Starburst-AGN composite galaxies are more complicated than AGN, and the analysis of their multi-wavelength SEDs is more challenging. Given these, we have built BayeSED, a general purpose tool for doing Bayesian analysis of SEDs by using whatever pre-existing model SED libraries or their linear combinations. The artificial neural networks (ANNs), principal component analysis (PCA) and multimodal nested sampling (MultiNest) techniques are employed to allow a highly efficient sampling of posterior distribution and the calculation of Bayesian evidence. As a demonstration, we apply this tool to a sample of hyperluminous infrared galaxies (HLIRGs). The Bayesian evidences obtained for a pure Starburst, a pure AGN, and a linear combination of Starburst+AGN models show that the Starburst+AGN model have the highest evidence for all galaxies in this sample. The Bayesian evidences for the three models and the estimated contributions of starburst and AGN to infrared luminosity show that HLIRGs can be classified into two groups: one dominated by starburst and the other dominated by AGN. Other parameters and corresponding uncertainties about starburst and AGN are also estimated by using the model with the highest Bayesian evidence. We found that the starburst region of the HLIRGs dominated by starburst tends to be more compact and has a higher fraction of OB star than that of HLIRGs dominated by AGN. Meanwhile, the AGN torus of the HLIRGs dominated by AGN tend to be more dusty than that of HLIRGs dominated by starburst. Overall, we believe that BayeSED could be a reliable and efficient tool for exploring the nature of complex systems such as dust-obscured Starburst-AGN composite systems from decoding their SEDs. |
| 学科主题 | 天文学 |
| 语种 | 中文 |
| 页码 | 156 |
| 源URL | [http://ir.ynao.ac.cn/handle/114a53/4667]  |
| 专题 | 云南天文台_大样本恒星演化研究组 |
| 推荐引用方式 GB/T 7714 | 韩云坤. 尘埃遮蔽的Starburst-AGN复合星系的能谱研究[D]. 北京. 中国科学院研究生院（云南天文台）. 2012. |
入库方式： OAI收割
来源：云南天文台
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